News and Events

Does feature similarity facilitate attentional selection?

Publication Type:

Journal Article

Source:

Attention, perception & psychophysics, Volume 72, Number 8, p.2128–43 (2010)

URL:

http://www.springerlink.com/content/w251l1736q38k003/

Keywords:

Adult, Association, Attention, Discrimination (Psychology), Female, Humans, Male, Motion Perception, Orientation, Pattern Recognition, Psychophysics, Visual, Young Adult

Abstract:

Object-based attention enables us to simultaneously select and report two features from the same visual object. Does feature-based attention contribute similarly to visual selection? In the present study, we investigated the concurrent discrimination of two motion fields with a divided attention paradigm. We found that dual-task performance improved when the two fields conformed to a continuous optic flow, consistent with "object-based" selection. However, we found no such improvement when the two motion fields were merely similar, as would have been expected from "feature-based" selection. Therefore, feature similarity does not facilitate attentional selection in the same way as belonging to the same object does.

Selectivity for polar, hyperbolic, and Cartesian gratings in macaque visual cortex

Publication Type:

Journal Article

Source:

Science, Volume 259, Number 5091, p.100–103 (1993)

URL:

http://www.sciencemag.org/content/259/5091/100.abstract

Abstract:

The neural basis of pattern recognition is a central problem in visual neuroscience. Responses of single cells were recorded in area V4 of macaque monkey to three classes of periodic stimuli that are based on spatial derivative operators: polar (concentric and radial), hyperbolic, and conventional sinusoidal (Cartesian) gratings. Of 118 cells tested, 16 percent responded significantly more to polar or hyperbolic (non-Cartesian) gratings than to Cartesian gratings and only 8 percent showed a significant preference for Cartesian gratings. Among cells selective for non-Cartesian gratings, those that preferred concentric gratings were most common. Cells selective for non-Cartesian gratings may constitute an important intermediate stage in pattern recognition and the representation of surface shape.

Bistable perception modeled as competing stochastic integrations at two levels.

Publication Type:

Journal Article

Source:

PLoS computational biology, Volume 5, Number 7, p.e1000430 (2009)

URL:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2700962&tool=pmcentrez&rendertype=abstract

Keywords:

Algorithms, Binocular, Binocular: physiology, Models, Neurological, perception, Perception: physiology, Photic Stimulation, Stochastic Processes, Time Factors, Vision

Abstract:

We propose a novel explanation for bistable perception, namely, the collective dynamics of multiple neural populations that are individually meta-stable. Distributed representations of sensory input and of perceptual state build gradually through noise-driven transitions in these populations, until the competition between alternative representations is resolved by a threshold mechanism. The perpetual repetition of this collective race to threshold renders perception bistable. This collective dynamics - which is largely uncoupled from the time-scales that govern individual populations or neurons - explains many hitherto puzzling observations about bistable perception: the wide range of mean alternation rates exhibited by bistable phenomena, the consistent variability of successive dominance periods, and the stabilizing effect of past perceptual states. It also predicts a number of previously unsuspected relationships between observable quantities characterizing bistable perception. We conclude that bistable perception reflects the collective nature of neural decision making rather than properties of individual populations or neurons.

Improved fluorescent compounds for tracing cell lineage.

Publication Type:

Journal Article

Source:

Developmental biology, Volume 109, Number 2, p.509–14 (1985)

URL:

http://www.sciencedirect.com/science/article/pii/0012160685904762

Keywords:

Amines, Amines: chemical synthesis, Animals, Dextrans, Dextrans: chemical synthesis, Embryo, Fluoresceins, Fluoresceins: chemical synthesis, Fluorescent Dyes, Fluorescent Dyes: chemical synthesis, Leeches, Leeches: embryology, Nonmammalian, Nonmammalian: cytology, Rhodamines, Rhodamines: chemical synthesis, Xenopus laevis, Xenopus laevis: embryology

Abstract:

In this note simple methods for the synthesis of several new fluorescent cell lineage tracers are described. These are fluorescent dextrans with average molecular weights of approximately 11 X 10(3), and with one or more fluorophore molecules covalently coupled to each dextran chain. These fluorescent dextrans are brighter than commercially obtainable products, and can be microinjected using either air-pressure injection or iontophoresis. They are long-lasting and have a uniform distribution in the cytoplasm of embryonic cells, clearly revealing very fine cell extensions such as cilia, axons, and filipodia. A method is also described for covalently attaching free amino groups to fluorescent dextran to make the tracers cofixable with cellular constituents by aldehyde treatment. Fluorescent dextran-amine tracers allow embryonic cell lineages to be studied in fixed, permeabilized, or sectioned embryos.

A Simple Recurrent Network for Implicit Learning of Temporal Sequences

Publication Type:

Journal Article

Source:

Cognitive Computation, Springer New York, Volume 2, Number 4, p.265–271 (2010)

URL:

http://www.springerlink.com/index/10.1007/s12559-010-9066-z

Keywords:

associations á, elman network á sequence, learning á, reinforcement learning á visuo motor

Abstract:

A behavioural paradigm for learning arbitrary visuo-motor associations established that human observers learn to associate visual objects with their corresponding motor responses faster if the objects follow a temporal rule rather than if they were presented in a random order. Here, we use a simple recurrent network with a back propagation training algorithm adapted to a reinforcement learning scheme. Our simulations fit quantitatively as well as qualitatively to the behavioural results, endorsing the role of temporal context in associative learning scenarios.

Temporal context and conditional associative learning.

Publication Type:

Journal Article

Source:

BMC neuroscience, Volume 11, p.45 (2010)

URL:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2873591&tool=pmcentrez&rendertype=abstract

Keywords:

Adult, Algorithms, Association Learning, Association Learning: physiology, Computer Simulation, Conditioning (Psychology), Conditioning (Psychology): physiology, Female, Fractals, Humans, Mathematical Concepts, Models, Neuropsychological Tests, Photic Stimulation, Psychomotor Performance, Psychomotor Performance: physiology, Reaction Time, Reaction Time: physiology, Statistical, Time Factors, Time Perception, Time Perception: physiology, Visual Perception, Visual Perception: physiology, Young Adult

Abstract:

We investigated how temporal context affects the learning of arbitrary visuo-motor associations. Human observers viewed highly distinguishable, fractal objects and learned to choose for each object the one motor response (of four) that was rewarded. Some objects were consistently preceded by specific other objects, while other objects lacked this task-irrelevant but predictive context.

Popout modulates focal attention in the primary visual cortex.

Publication Type:

Journal Article

Source:

NeuroImage, Volume 22, Number 2, p.574–82 (2004)

URL:

http://www.sciencedirect.com/science/article/pii/S1053811904000746

Keywords:

Adult, Attention, Attention: physiology, Brain Mapping, Brain Mapping: methods, Computer-Assisted, Cues, Eye Movements, Eye Movements: physiology, Hemodynamics, Hemodynamics: physiology, Humans, Image Processing, Magnetic Resonance Imaging, Magnetic Resonance Imaging: methods, Male, Neurons, Neurons: physiology, Orientation, Reproducibility of Results, Retina, Retina: physiology, Visual Cortex, Visual Cortex: physiology, Visual Fields, Visual Fields: physiology

Abstract:

The influence of context-dependent interactions on attention-related neural activity was studied in the human primary visual cortex (V1) with event-related fMRI. Retinotopic field-sign mapping was used to determine the localization of V1 with respect to adjacent retinotopic areas. Observers reported the orientation of a Gabor patch at pre-cued extrafoveal locations when it was salient among distractor Gabors and when it was not. Saliency was caused by local orientation contrast between Gabors-a mechanism that is thought to arise from context-dependent interactions in the V1 proper. A comparison of the attention-related BOLD response for salient and non-salient stimuli in V1 revealed that salient Gabors caused a significantly smaller BOLD response than non-salient Gabors. This differential effect was not observed in higher-order visual areas (V3/V3A, MT+/LO, IPS). When attention was not focused onto the target, the size of the BOLD response was generally reduced in all visual areas, and no difference was seen in V1 for salient and non-salient Gabors. These findings suggest that contextual interactions underlying saliency influence attentional modulations in V1 and support the view that perceptual and attentional mechanisms share neural circuits at this early stage of visual processing.

Cortical response to task-relevant stimuli presented outside the primary focus of attention.

Publication Type:

Journal Article

Source:

Journal of cognitive neuroscience, Volume 22, Number 9, p.1980–92 (2010)

URL:

http://www.mitpressjournals.org/doi/abs/10.1162/jocn.2009.21327

Keywords:

Adult, Attention, Attention: physiology, Cerebral Cortex, Cerebral Cortex: physiology, Female, Humans, Magnetic Resonance Imaging, Magnetic Resonance Imaging: methods, Male, Photic Stimulation, Photic Stimulation: methods, Psychomotor Performance, Psychomotor Performance: physiology, Reaction Time, Reaction Time: physiology, Visual Cortex, Visual Cortex: physiology, Visual Perception, Visual Perception: physiology, Young Adult

Abstract:

Visual attention selectively enhances the neural response to a task-relevant item. But what happens when an item outside the primary focus of attention is also relevant to the task at hand? In a dual-task fMRI experiment, we studied the responses in retinotopically organized visual cortex in such a situation. Observers performed an attention-demanding task in the fovea while another, unmasked stimulus appeared in the visual periphery. With respect to this latter stimulus, observers attempted to perform either a less or a more attentionally demanding task. Both tasks increased the BOLD response to the peripheral stimulus. Behaviorally, however, only the less demanding task was performed well, whereas the demanding task was carried out near chance. What could explain the discrepancy between BOLD response and behavioral performance? A control experiment revealed that the report of the less demanding feature was severely disturbed by a mask. Moreover, the visual attributes queried by the demanding task had a significantly shorter iconic memory persistence. We conclude that, in the dual-task situation, the focus of attention initially remains with the foveal task, but subsequently shifts to the former location of the peripheral stimulus. Such a belated shift to a peripheral iconic memory (futile in one case, informative in the other) would reconcile the similar BOLD response with the disparate behavioral performance. In summary, our results show that an enhanced BOLD response is consistently associated with attentional modulation, but not with behavioral performance.

Matching of visual input to only one item at any one time.

Publication Type:

Journal Article

Source:

Psychological research, Volume 73, Number 3, p.317–26 (2009)

Keywords:

Adolescent, Adult, Female, Humans, Male, Memory, Models, Pattern Recognition, Psychological, Signal Detection, Visual

Abstract:

When we perform a visual search we know what we are looking for and determine where it is. A representation of the object in our working memory, the 'search-template', is compared to the items in the scene until a match is found. So far it is unknown whether observers can search for multiple items at the same time. Here we compare the performance of subjects between a task in which they search for one of two target-items in a stream of visual objects and a task with only a single target. We find that search is effectively limited to one item at a time. This limitation occurs for simple and complex objects and even if the subjects have to look for two features from different domains. We conclude that matching has a fundamental capacity-limitation as the visual input can be matched to only one search-template at a time.

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